U.S. patent application number 11/065209 was filed with the patent office on 2005-06-30 for load sensor with use of crystal resonator.
This patent application is currently assigned to Yamato Scale Co., Ltd.. Invention is credited to Adachi, Motoyuki, Chiba, Akio, Ono, Kozo, Yamanaka, Masami.
Application Number | 20050139016 11/065209 |
Document ID | / |
Family ID | 19016488 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050139016 |
Kind Code |
A1 |
Yamanaka, Masami ; et
al. |
June 30, 2005 |
Load sensor with use of crystal resonator
Abstract
Excitation electrodes are respectively affixed to central
portions of both surfaces of a long plate-shaped AT-cut crystal
resonator, the central portion starts a thickness shear oscillation
in the length direction of the crystal resonator when an electric
signal is applied to the central portion of the crystal resonator
through the excitation electrodes. And, channel-shaped,
half-circular-shaped, or trapezoid grooves in cross-section are
respectively formed in the plate width direction on middle portions
between the center portion and end portions of the crystal
resonator. These grooves are formed so as to be symmetrical with
respect to a thicknesswise central position of the crystal
resonator through a well-known etching technique such as
photo-etching and the like.
Inventors: |
Yamanaka, Masami;
(Akashi-shi, JP) ; Adachi, Motoyuki; (Akashi-shi,
JP) ; Chiba, Akio; (Sayama-shi, JP) ; Ono,
Kozo; (Sayama-shi, JP) |
Correspondence
Address: |
ALLEMAN HALL MCCOY RUSSELL & TUTTLE LLP
806 SW BROADWAY
SUITE 600
PORTLAND
OR
97205-3335
US
|
Assignee: |
Yamato Scale Co., Ltd.
Nihon Dempa Kogyo Co., Ltd.
|
Family ID: |
19016488 |
Appl. No.: |
11/065209 |
Filed: |
February 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11065209 |
Feb 22, 2005 |
|
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|
10163858 |
Jun 5, 2002 |
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6880407 |
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Current U.S.
Class: |
73/862.59 |
Current CPC
Class: |
G01G 3/13 20130101 |
Class at
Publication: |
073/862.59 |
International
Class: |
G01L 001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 11, 2001 |
JP |
2001-175327 |
Claims
What is claimed is:
1. A load sensor with use of a crystal resonator comprising: a flat
plate-shaped crystal resonator for oscillating in a thickness shear
oscillation mode; and supporting bodies for supporting the crystal
resonator; wherein the crystal resonator is retained between the
supporting bodies which are respectively in contact with and
pressing opposing end faces of the crystal resonator in a direction
of a thickness shear oscillation of he outside of the crystal
resonator; wherein the end faces are configured to minimize the
areas contacting the supporting bodies as much as possible, such
that the supporting bodies contact the end faces along less than an
entire thickness of the end faces; and wherein a load is measured
based on change in an oscillation frequency of the thickness shear
oscillation of the crystal resonator generated in proportion to the
load acted thereon through the supporting bodies.
2. The load sensor with use of a crystal resonator according to
claim 1, wherein the end faces are circular-arc-shaped, being
curved in a thickness direction of the crystal resonator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of U.S. patent application
Ser. No. 10/163,858 entitled LOAD SENSOR WITH USE OF CRYSTAL
RESONATOR, filed Jun. 5, 2002, now pending, which in turn claims
priority to Japanese Patent Application No. 2001-175327, filed on
Jun. 11, 2001. The entire disclosure of each of these applications
is herein incorporated by reference for all purposes.
FIELD OF THE INVENTION
[0002] The present invention relates to a load sensor using a
crystal resonator for measuring a load, and more specifically to a
load sensor capable of minimizing as much as possible outward
leakage of oscillation energy of a thickness shear oscillation
caused by a crystal resonator.
BACKGROUND OF THE INVENTION
[0003] Strain-gauge load cells have been widely used as a load
sensor for electronic weighing scales. However, in these years,
with rapid advance in electronic measurement technologies, load
sensors which are more accurate than the strain-gauge load cells
have been developed. Of these load sensors, different types such as
a tuning fork type, a string oscillation type, a gyroscope type,
and the like, have already been put into practical use.
[0004] Incidentally, as such a load sensor with a high degree of
accuracy, an oscillation-type load sensor using a quartz resonator
has been proposed. This load sensor takes advantage of the
phenomenon that the oscillation frequency of an AT-cut quartz plate
piece which is under thickness shear oscillation excited by
exciting means, varies in proportion to a force applied to the
quartz piece parallel to a plate face thereof. The quartz resonator
has advantages such as less temperature dependency, oscillation
with stable frequency, and inexpensiveness. For these reasons, the
use of the quartz resonator makes it possible to attain a load
sensor which is higher in accuracy and lower in cost as compared to
load sensors described above, such as the tuning fork type, the
string oscillation type, the gyroscope type, and the like.
[0005] FIG. 8 is a perspective view showing a constitution of basic
parts of a conventional load sensor using a quartz resonator. In
FIG. 8, a quartz plate resonator 300 is a quartz piece which
oscillates in a thickness shear oscillation mode in the length
direction. Electrodes 301, 301 are respectively affixed to both
faces of the quartz resonator 300, and these electrodes 301, 301
are connected to an oscillation circuit (not shown) which
oscillates in proportion to the oscillating frequency of the quartz
resonator 300.
[0006] As shown in FIG. 8, grooves which are rectangular in
cross-section are formed at end portions of supporting bodies 302,
302 which support the quartz resonator 300 throughout the plate
widths. And, the quartz resonator 300 is retained by the supporting
bodies 302, 302 in the thickness direction by fitting both of the
end portions of the quartz resonator 300 into the grooves.
[0007] In the load sensor thus constructed, when a load W is
applied on the quartz resonator 300 in the compressing direction,
the oscillation frequency of the quartz resonator 300 changes in
proportion to the load W, and then the oscillation frequency of the
above-described oscillation circuit changes in proportion to the
change. The load W is measured by detecting this change in the
oscillation frequency.
[0008] In some cases, both of the end portions of the quartz
resonator 300 and the grooves formed at the ends of the supporting
bodies 302, 302 may be fixed to each other by use of adhesive or
the like. In these cases, since the quartz resonator 300 remains
fixed even if the supporting bodies 302, 302 move away from each
other, a load W applied in the pulling direction can also be
measured.
[0009] However, as described above, when both of the end portions
of the quartz resonator 300 are supported by the supporting bodies
302, 302, the thickness shear oscillation of the quartz resonator
300 in the length direction is restrained, thereby causing loss of
the oscillation energy. Due to this, there exists such a problem
that its Q (Quality factor) as an oscillator decreases.
[0010] Furthermore, since the thickness shear oscillation of the
quartz resonator 300 is transmitted to the supporting bodies 302,
302, thereby causing the surrounding mechanism to resonate, there
exists such a problem that measurements can not be performed with a
high degree of accuracy.
SUMMARY OF THE INVENTION
[0011] The present invention has been developed under these
circumstances, and an object thereof is to provide a load sensor
with use of a crystal resonator which has high Q of the crystal
resonator and is capable of performing measurements with a high
degree of accuracy, which measurements are achieved by supporting
the crystal resonator so as not to restrain the thickness shear
oscillation and so as to minimize the oscillation transmitted to
the supporting bodies.
[0012] In order to solve the above-described problems, a load
sensor using a crystal resonator comprises: a long plate-shaped
crystal resonator; supporting bodies for respectively supporting
both lengthwise end portions of the crystal resonator; and exciting
means for exciting a thickness shear oscillation at a center
portion of the crystal resonator in the length direction, wherein
middle portions whose thickness is smaller than that of the center
portion are respectively provided between the center portion and
both of the end portions and a load is measured based on the change
in an oscillation frequency of the thickness shear oscillation of
the center portion of the crystal resonator generated in proportion
to the load acted thereon through the supporting bodies.
[0013] According to the present invention, since the thickness of
the middle portion is smaller than that of the center portion, even
if the thickness shear oscillation is excited by the exciting means
at the center portion of the crystal resonator, the oscillation is
not easily transmitted to both of the end portions. For this
reason, the oscillation transmitted to the supporting bodies
supporting both of these end portions can be reduced. Therefore, it
is possible to restrain the surrounding mechanism from resonating
and to realize more accurate measurements, compared to the
conventional load sensor.
[0014] Furthermore, in the present invention, the central portion
can be configured to form symmetrical grooves with respect to a
thicknesswise central position of the crystal resonator. When the
thickness shear oscillation of the crystal resonator is generated,
both surfaces thereof move most, but not the thicknesswise central
position of the crystal resonator. Therefore, the formation of the
symmetrical grooves with respect to the thicknesswise central
position will set relatively most moving portions free, thereby
reducing oscillation energy loss of the crystal resonator and thus
increasing Q as an oscillator, as compared to the conventional load
sensor.
[0015] Furthermore, a load sensor using a crystal resonator
comprises: a flat plate-shaped crystal resonator for oscillating in
a thickness shear oscillation mode and supporting bodies for
supporting the crystal resonator, wherein the crystal resonator is
retained between the supporting bodies which are respectively in
contact with and pressing opposing end faces of the crystal
resonator from the outside of the crystal resonator, the end faces
are configured to minimize the areas contacting the supporting
bodies as much as possible, and a load is measured based on change
in an oscillation frequency of the thickness shear oscillation of
the crystal resonator generated in proportion to the load acted
thereon through the supporting bodies.
[0016] According to the present invention, since the opposing end
faces of the crystal resonator are configured to minimize as much
as possible the areas that the supporting bodies are in contact
with and pressing, the transmission of the thickness shear
oscillation of the crystal resonator to the supporting bodies can
be minimized as much as possible. Therefore, it is possible to
restrain the surrounding mechanism from resonating and to realize
more accurate measurements, as compared to the conventional load
sensor. What is more, the fabrication of the crystal resonator is
simpler for the present invention than for the above described
invention.
[0017] Even furthermore, in the above-described invention, the end
faces may be circular-arc-shaped. By doing so, the areas of the
opposing end faces that the supporting bodies are in contact with
and pressing can be minimized, and when the crystal resonator
oscillates in the thickness shear oscillation mode, relatively most
moving portions can be set free.
[0018] This object, as well as other objects, features and
advantages of the present invention will become more apparent to
those skilled in the art from the following description taken with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIGS. 1A-1C are perspective views showing a crystal
resonator used in a load sensor according to Embodiment 1 of the
present invention;
[0020] FIGS. 2A and 2B are perspective views showing the load
sensor according to Embodiment 1 of the present invention;
[0021] FIG. 3 is a side elevation view showing in detail a
constitution of an electronic scale with use of the load sensor
according to Embodiment 1 of the present invention;
[0022] FIG. 4 is a perspective view showing a constitution of a
crystal resonator and supporting bodies used in the electronic
scale shown in FIG. 3;
[0023] FIG. 5 is a functional block diagram showing an example of a
constitution of the electronic scale using the load sensor
according to Embodiment 1 of the present invention;
[0024] FIG. 6 is a functional block diagram showing an example of a
constitution of the electronic scale using the load sensor
according to Embodiment 1 of the present invention;
[0025] FIGS. 7A and 7B are perspective views showing a constitution
of a load sensor using a crystal resonator according to Embodiment
2 of the present invention; and
[0026] FIG. 8 is a perspective view showing a constitution of the
basic parts of the conventional load sensor using a crystal
resonator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Hereinbelow, preferred embodiments of the present invention
will be described with reference to drawings.
Embodiment 1
[0028] FIGS. 1A-1C are perspective views showing a crystal
resonator used in a load sensor according to Embodiment 1 of the
present invention. In FIGS. 1A-1C, a long-plate shape crystal
resonator 1 is an AT-cut quartz piece capable of oscillating in a
thickness shear oscillation mode in a length direction of the
quartz resonator 1.
[0029] Excitation electrodes 2, 2 serving as exciting means are
respectively affixed to both surfaces of a central portion la of
the quartz resonator 1. The central portion 1a starts the thickness
shear oscillation in the length direction of the crystal resonator
1 when an electric signal is supplied to the central portion la of
the crystal resonator 1 through the excitation electrodes 2, 2. It
should be noted that these electrodes 2, 2 are connected to an
oscillation circuit described below.
[0030] As shown in FIG. 1A, channel-shaped grooves in cross-section
are respectively provided in the plate width direction on both
surfaces of middle portions 1c, 1c, which are located between the
center portion 1a and end portions 1b, 1b of the crystal resonator
1. These grooves are formed so as to be symmetrical with respect to
a thicknesswise central position of the crystal resonator 1 by use
of a well-known etching technique, such as photo etching and the
like.
[0031] Thus, since the grooves are formed on the middle portions
1c, 1c, the thickness of the middle portions 1c, 1c is smaller than
the thickness of the central portion 1a. Because of that, even if
the central portion 1a oscillates in the thickness shear
oscillation mode, its oscillation is not easily transmitted to both
of the end portions 1b, 1b.
[0032] Furthermore, as described before, since the grooves are
formed so as to be symmetrical with respect to the thicknesswise
central position of the crystal resonator 1, those portions of the
plate to be moved most when the thickness shear oscillation is
generated are set free. Because of this, the thickness shear
oscillation can be restrained, thereby reducing the amount of
oscillation energy loss.
[0033] While the channel-shaped grooves in cross-section are
provided in the plate width direction on the middle portions 1c, 1c
of the crystal resonator 1, as described before, these grooves are
not limited to this shape and may be of any shape insofar as they
are formed to be symmetrical with respect to the thicknesswise
central position of the crystal resonator 1. Therefore, the shape
may be, for example, of half-circle shape in cross-section as shown
in FIG. 1B, or of trapezoid-shape in cross-section as shown in FIG.
1C.
[0034] FIGS. 2A and 2B are perspective views showing load sensors
according to Embodiment 1 of the present invention. As the arrows
in the figure show, FIG. 2A shows a load sensor which can measure a
load only in the compressing direction of the load W, and FIG. 2B
shows a load sensor which can measure a load both in the
compressing and pulling directions of the load W. It should be
noted that, while FIGS. 2A and 2B show the load sensor with use of
the crystal resonator 1 shown in FIG. 1C, it is needless to say
that the crystal resonator shown in FIG. 1A or 1B may be used
instead.
[0035] In FIG. 2A, rectangular grooves in cross-section are formed
at the end portions of the supporting bodies 3, 3 throughout the
plate width, and the crystal resonator 1 is supported by
respectively fitting both of the end portions 1b, 1b of the crystal
resonator 1 into these grooves. Supporting the crystal resonator 1
in the way described above enables the measurement of a load W in
its compressing direction.
[0036] On the other hand, in FIG. 2B, grooves are formed at end
portions of the supporting bodies 3, 3 throughout the plate widths,
whose shape enables the grooves of the supporting bodies to fit on
both of the end portions 1b, 1b and portions of the grooves formed
on both surfaces of the middle portions 1c, 1c of the crystal
resonator 1. Thus, the crystal resonator 1 is supported by
respectively fitting the grooves of the supporting bodies on both
of the end portions 1b, 1b and the portions of the grooves formed
on both of the surfaces of the middle portions 1c, 1c. In this way,
since not only both of the end portions 1b, 1b, but also the
portions of the grooves of the crystal resonator are fit in the
grooves of the supporting bodies, the crystal resonator 1 does not
fall away even if the supporting bodies 3, 3 move in the detaching
direction. Therefore, as shown by the arrows, a load W can be
measured not only in the compressing direction but also in the
pulling direction without using an adhesive utilized in the
conventional load sensor.
[0037] As described before, the oscillation circuit 21 is connected
to the excitation electrodes 2, 2. This oscillation circuit 21
oscillates in proportion to an oscillation frequency of the
thickness shear oscillation of the central portion 1a of the
crystal resonator 1. If a load W is applied through the supporting
bodies 3, 3, the oscillation frequency of the central portion 1 a
should vary, and then the oscillation frequency of the oscillation
circuit 21 should also vary accordingly.
[0038] FIG. 3 is a side elevation view showing a constitution of an
electronic scale with a load sensor according to the present
invention. FIG. 4 is a perspective view showing in detail a
constitution of the crystal resonator 1 and the supporting bodies
3, 3 which are used in the electronic scale. As shown in FIG. 3,
the electronic scale 10 is configured such that a tray 11 used to
receive a load W is supported through the so-called Roberval's
mechanism. This Roberval's mechanism comprises a fixed pole 12
fixed to a base table B, a movable pole 13 for supporting the tray
11 described above, and upper and lower beams 14, 14 arranged to be
parallel to each other.
[0039] Levers 15, 15 are respectively provided at and protruded
inwardly from an upper portion of the fixed pole 12 and a lower
portion of the movable pole 13, and the supporting bodies 3, 3 for
supporting the crystal resonator 1 are respectively attached to tip
portions of the levers 15, 15.
[0040] Half-circle-shaped cutout portions are respectively provided
at upper and lower portions of the beams 14, 14, and the thickness
between the upper and lower cutout portions is small. Because of
this, when the movable pole 13 moves downwardly due to a load W,
the beams 14, 14 should be bent downwardly in proportion to the
move. By controlling the extent of the bend, the parallel relation
between the beams 14, 14 can be maintained.
[0041] In the electronic scale 10 thus constructed, when a load W
is applied onto the tray 11, the movable pole 13 moves downwardly
in proportion to the load W. Although the lever 15 provided at the
side of the movable pole 13 also moves downwardly in proportion to
this move, the lever 15 provided at the side of the fixed pole 12
does not move but remains still. Thus, a pulling force in
proportion to the load W will act on the crystal resonator 1.
[0042] As shown in FIG. 4, the crystal resonator 1 used in the
electronic scale 10 is supported by the supporting bodies 3, 3 in
the manner described before with reference to FIG. 2B. These
supporting bodies 3, 3 are respectively connected to the levers 15,
15, and flexures 16, 16 are formed at the connected portions. By
providing the flexures 16, 16 as described above, even if an offset
load is applied to the tray 11, its influence can be minimized.
[0043] FIG. 5 is a functional block diagram showing a constitution
of the electronic scale 10. As described before, the oscillation
circuit 21 oscillates in proportion to an inherent frequency of the
thickness shear oscillation of the crystal resonator 1. And, a
counter 22 counts the oscillation frequency of the oscillation
circuit 21 during a predetermined period of time. It should be
noted that the counter 22 counts through offsetting the oscillation
frequency of the oscillation circuit 21 when zero load W is applied
to the tray 11. Therefore, only a varied amount responsible for the
load W can be counted.
[0044] A converting portion 23 converts the counted values from the
counter 22 into weight data. In this case, the converting portion
23 performs such calculations through multiplications of the
gravitational acceleration and a variety of proportionality
factors, etc., that the converted value becomes equivalent to the
weight data obtained when standard weights are placed on the tray
11.
[0045] An output portion 24 is comprised of a liquid crystal
display, a printer, or the like, and displays, prints, etc., the
weight data outputted by the converting portion 23.
[0046] Incidentally, when the electronic scale 10 is thus
constructed, there might arise such problems that measurement of a
load W can not be completed within real time, the resolution is not
of practical size, and the like. Therefore, a constitution shown in
FIG. 6 is preferred.
[0047] In FIG. 6, a crystal resonator 100 is a quartz piece which
can oscillate at approximately 100 times as high a frequency as the
crystal resonator 1 and be located at such an adequate place that
the influence from a load W is ignored even when the load W is
applied to the tray 11. Similarly to the crystal resonator 1,
excitation electrodes 200, 200 are respectively affixed to central
portions of both surfaces of this crystal resonator 100. And, these
excitation electrodes 200, 200 are connected to an oscillation
circuit 41, and the oscillation circuit 41 oscillates in proportion
to an inherent frequency of the crystal resonator 100.
[0048] A first counter 31 counts an integer cycle of an oscillation
frequency of the oscillation circuit 21. And, a gate circuit (not
shown) that a second counter 42 has is opened or closed according
to the counted integer cycle.
[0049] The second counter 42 counts an oscillation period of the
oscillation circuit 41 while the gate circuit is open. In this
case, as a load W increases, that is, as the oscillation frequency
of the oscillation circuit 21 increases, the length of time that
the gate circuit is open is reduced. Because of this, the counted
value of the second counter 42 is inversely proportional to the
value of the load W. It should be noted that, similarly to the
counter 22 described before, the second counter 42 also counts
through offsetting the oscillation frequency of the oscillation
circuit 41 when the load W is zero.
[0050] A first converting portion 43 calculates a reciprocal number
of the period counted by the second counter 42, that is, the
frequency. And, a second converting portion 44 processes the
conversion from frequencies to weight data, similarly to the
converting portion 23 described above. The resulting weight data
are displayed or printed by an output portion 45.
[0051] When the crystal resonator 100 is provided in addition to
the crystal resonator 1 in a manner described thus far, it becomes
possible to obtain weight data with high resolution within real
time.
Embodiment 2
[0052] FIGS. 7A and 7B are perspective views showing a constitution
of a load sensor with a crystal resonator according to Embodiment 2
of the present invention. In FIG. 7A, a crystal resonator 4 is a
rectangular AT-cut quartz piece and retained between rectangular
parallelepiped supporting bodies 6, 6 which are respectively in
contact with and pressing end faces of one end portion and the
other opposing end portion thereof from the outside. The end faces
are filed so as to be circular-arc-shaped in cross-section. Since
the other elements are identical to those of Embodiment 1, the same
or corresponding parts are denoted by the same reference numerals
and as such will be not described herein.
[0053] Since the end faces of the crystal resonator 4 are
circular-arc-shaped, the contacting areas with the supporting
bodies 6, 6 are smaller as compared with the case where the end
faces are flat. Because of this, when the crystal resonator 4
oscillates in the thickness shear oscillation mode, the oscillation
transmitted to the supporting bodies 6, 6 can be minimized, thereby
restraining the surrounding mechanism from resonating. Furthermore,
since it is also possible to set relatively most moving portions
free, high Q can be attained.
[0054] Furthermore, a crystal resonator 7 shown in FIG. 7B is a
circular AT-cut quartz piece. To form opposing end faces, end
portions of this crystal resonator 7 are cut along two adequate
parallel lines orthogonal to the oscillating direction of the
thickness shear oscillation. The end faces thus formed are shaped
to be a circular-arc shape similarly to the one described before.
Therefore, the same effects described before can be obtained.
[0055] Since circular crystal pieces are generally widely
available, the use of such a crystal piece enables the load sensor
of the present invention to be implemented easily and at a low
cost.
[0056] The load sensor thus constructed according to Embodiment 2
of the present invention can be applied to electronic scales
similarly to Embodiment 1.
[0057] Numerous modifications and alternative embodiments of the
invention will be apparent to those skilled in the art in view of
the forgoing description. Accordingly, the description is to be
construed as illustrative only, and is provided for the purpose of
teaching those skilled in the art the best mode of carrying out the
invention. The details of the structure and/or function may be
varied substantially without departing from the spirit of the
invention.
* * * * *